Mid-grade gas
 

Well, I wasn't in the neighborhood of my usual gas station where premium sells for 10 cents a gallon over regular.

So for the first time ever in a MB owned car, I opted for mid-grade.

Even though we have some of the cheapest prices in the country for gas, I just couldn't pay $2.17 a gallon for premium.

We'll see how it goes. Typically I get between 19 and 20 mpg in my mixed driving week.

1989 300e 151k miles.

Depends on the engine. My 260E with 9.0 CR runs just fine on regular. Has for years. With higher CR or maybe super/turbocharged, it might matter. then again, most of theose engines have knock sensors. you'll never notice a difference.

KE-equipped engines of that era don't have knock sensors. Most will run on regular unleaded without detonation, especially in cool weather and coolant temperatures below 90C. In warmer temperatures or at higher coolant temperatures there may be some transient detonation at low revs/high load.

The specified CR of M103s in US models is 9.2:1.

Duke

$2.17 for premium would look good here in Oregon. That's about what we pay for regular and premium is up around $2.39. :eek: I'm also thinking about using a lower octane fuel around town.

I run midgrade in the winter. No troubles.

$2.17 for premium is a real good price! :D I think it is in the $2.30 range up hear.

Not to hijack this thread, but..... premium here is over $2.50 a gallon. Marathon's refinery is here - not 4 miles from my house.

You're more likely to get detonation "around town" than at highway speed including passing, since "around town" is when the engine is most likely to see the low rev/high load condition and higher coolant temperatures, which are the most likely conditions for detonation.

Duke

And we have it good here in the U.S. I've been in the UK on business a couple of times this year. On the way to a customer visit we stopped to fill up my coworker's car - a BMW 320D. Diesel was 95 pence per liter - the tab came to 14 Pounds for 15 liters. Thats about $28 for 4 gallons of fuel! A full tank costs almost $100.

On the plus side, a 3-series with a modern common rail diesel has surprisingly good performance and delivers better than 40MPG on the motorway.

- JimY

i have been paying around 2.59/gallon of premium lately.

last tank cost me close to 60 bucks. i think it was ~57 and change.

$0.10 per GALLON difference? We pay 12 cents per LITRE more for premium, which is about 45 cents per gallon.

Is this false economy? How much money are you going to save? Gasoline is not a major cost of operating a car. Depreciation is king!

Okay, suppose you drive 15,000 miles per year and get 20mpg. You burn 750 gallons of gas per year. That 10 cents difference adds up to a total of $75.00 PER YEAR or about $6.25 per month.

SIX BUCKS a month you're trying to save. Don't stop at StarBucks tomorrow.

Hey man...... I change my own oil, do all of my own repairs...... I am just seeing how the car runs on mid-grade.....

BTW, I make my own coffee in the morning as well.

That said, 50 weeks of the year I should be able to pass by my usual place and put premium in.

My car is probably darn near fully depreciated anyway.

Lee
Greenville, SC

Actually I think the manual says 91 octane and over is the recommended fuel.
Since most premium around here is 93 octane, I suppose one could mix a few gallons of 89 octane or even 87 octane with, say 3/4 tank of premium and still be over 91 octane, if it all mixed, totally evenly.
Not that I would ever do it with one of my Mercedes that has that "Premium Unleaded Gasoline Only" in black and white right under the fuel guage.
I paid 2.199 for the cheapest Hess premium in the area tonight, and regular was 2.039. That's 16 cents a gallon more than regular. Some stations are 21 cents more for premium; wow. I could save two bucks a tankful if it took regular, but I'd rather splurge a bit and not worry about pinging, knock, preignition, fouling plugs with those little metal droplets, etc.
Personally I'd rather save two bucks a week by using a coupon or two for lunch or something....

If you do get detonation and you are happy with a little less power, you can change the resistor that is located near the master cylinder to allow for burning lower octane fuel.

The euro cars have a dial that selects a different resistor to adjust for different fuel grades. US cars have a fixed resistance there. If you pull out the resistor it gives max advance and max power, but you have to burn premium fuel. By putting in resistance you can retard timing and allow cheap fuel to be used without detonation.

That said, remember that if you do that so you can run cheap fuel, that fuel will not take you as far down the road as advanced timing and premium fuel.

Good luck,

I'm currently running 87 octane and no resistor, which is the most aggressive timing map, and I'm not getting any detonation, but the weather is still cool.

Duke

this cool weather thing has me intrigued....

however, like I said...my faviorite station sells premium for 10 cents a gallon over regular.... 5 over midgrade...

so I will likely be back at premium next fill.... the car runs perfect on mid-grade right now in South Carolina.... I am also told we get "good" gas here...whatever that means...

Lee

Mid grade
 

My E320 (104) runs just fine on mid grade. 25 MPG on the highway, mostly highway driving. I know it offends the purists.

I also knew you'd catch hell for quoting our SC fuel prices. We have always been about the lowest in the country.

I find it interesting that the price differential from regular to midgrade to premium is always 10¢ each step, no matter the price of regular. You'd think the differential would be a percentage. At these record prices, this makes filling with regular less attractive for engines designed to run on premium.

The Midwest has the highest prices in the continental US.

well...I went through the tank with mid-grade....

at 300 miles 14.6 gallons.... did slightly better than I usually do with premium... I am fairly consistent at about 300 miles a week in mixed driving..

filled up with mid-grade again... gas is about 10 cents a gallon more than last week....

Lower octane fuel contains slightly more energy. With the manual tranny, I get 25-27 mpg, about the same as my lighter weight 2.2L Honda Accord.
Pretty amazing really.

Although I agree with you on the energy issue, the experts here will not agree.

well, I am likely to stick with mid-grade until it gets hot or I detect any type of engine ping.

a co-worker has a 1991 300SpensivE. She has over 200k and uses nothing but mid-grade....

Larry,
Do you happen to have a chart of the different resistor values for the maps in the EZL? IIRC the installed resistor for U.S. is 200 ohms. I'm not so interestd in changing timing for lower grade fuel as I am in getting M103s to pass the ASM smog check. There is no way to retard timing on these as you well know. I've been using mid grade fuel in an 87 300E, 90 300E, 88 300SEL, 90 300SEL, and an 89 300CE without any problems, but I do use premium in the mountains.

Peter

I agree that lower octane gasoline MIGHT have greater energy. It will vary depending on the particular blend of gasoline required for each area/season, and at best it would only be about 1-2 percent, so measuring any decrease in fuel consumption would be difficult when you account for fill level and driving conditions variation.

Compounding the issue is the fact that oxygenated fuels have about 3 percent less energy than non-oxygenated fuels of the same octane number.

Duke

Switched from premium to mid-grade fuel two years ago. Mileage didn't change. Performance is slightly less but it is a 4700 lb truck with a v6. Never heard detonation and very familiar with the sound.

FR

Running 89 octane..
But when summer comes around, I run 91 because engine begins to knock.

Read my post in this thread and also go to the link that I provided in this thread:

http://www.peachparts.com/shopforum/showthread.php?p=833484#post833484

Lower octane fuel in the moutains will probably create less detonation tendency than in the flatlands due to the lower air density at higher altitudes. The emission test numbers I reported are with regular unleaded and the test was done near sea level on a mid-sixties degree day. No detonation during the test. The only time I get detonation - and it's just transient - is if I load the engine at low revs from a short shift, but this only occurs at coolant temps above about 90C or ambient temps above about 75F. Where you live you could probably not use regular during the summer.

I actually need to remap the ignition advance curves. Since I did the work I read in the service information that the timing map is altered above 95C (It doesn't specifiy how, but one can argue that the timing is increased to cool the engine or it is reduced to limit detonation, and I suspect the latter.) and the coolant temp did exceed this value during some of the testing.

If you short the R16/1 connector and block the vacuum advance you will get very good emission test numbers due to the significantly reduced timing under the test load conditions. The NOx numbers really surprised me. I expected them to be lower since the reduced ignition advance will reduce peak flame temperature, but the 90 percent reduction really suprised me.

The car ran fine, except for being sluggish below about 2000 and VERY SLUGGISH below 1500. Above 2500 there was little SOTP difference. The low rev loss of torque will probably be less noticeable on a model with an automatic transmission since converter slippage will not allow a high load below about 2000.

Duke

I just put gas in my car and it was $2.85 a gallon from premium. Mid Grade was $2.75 and Regular was $2.65.

The way I see it, lets say I put in 10 gallons, thats $28.50, if I put in mid grade thats $27.50 and if I put in regular thats $26.50

It really only adds up to a small difference in price for me. I would rather pay way less, but since the car states premium unleaded only, thats what I use, and I pay the price unfortunately.

I know all those extra cents adds up over the course of a year to a decent amount, but I have used mid grade in my car before and regular, and my gas mileage suffered quite a bit.

Alon